I think it isn't that your over qualified or failing the test. Maybe you have a much better personality than some of the nasty people working for TSA. I am sure they have to hire a large diversity in staff. Although I'm sure you will get extensive heat on that comment.

I worked for the airlines during 911 and most of us lost our jobs, became temp screeners until TSA came in. They did serious background checks on us and many lost their jobs over simple stuff like a hot check, unpaid ticket, etc. I couldn't believe some of the people who lost their jobs at the time (a 48 year old grandma who had an indecent exposure charge at 17 years old). You would think they must pass an extensive background check as well! Only about a 1/4 was taken back or asked to come back to the airlines on rehire about a year down the road and most of us had already gone somewhere else.